9th Feb Flashcards
What are prospective studies?
Record variables over the study period, with the outcome measured subseqeuntly
Cohort studies are usually prospective
What are retrospective studies?
Measure outcome and then look backwards to measure exposure and other variables
Case control and cross-sectional studies are retrospective
What are the pros and cons of prospective data collection?
Pros: fewer sources of bias, less chance of confounding, some data can only be measured prospectively
Cons: time and resource intensive, tendency to collect data on more variables than you need, subjects can drop out, usually unfeasible for rare outcomes
What are the pros and cons of retrospective data collection?
Pros: data collection is less time consuming and resource intensive, allows oversampling of rare outcomes
Cons: more susceptible to bias (recruitment and data recall), some variables cannot be measured directly, if data is from records there is little control over it
What are the issues with newly collected data?
Helps ensure you record all variables you need, applied consistently
More expensive/ time consuming
Harder to recruit
Ethical issues
What are the issues with existing data?
Limited choice as to which variables have been measured
Limited involvement in consistency of measurement
What is a proforma?
Method of data collection such as questionnaire
Ensures variables are measured consistently
What are sources of measurement error?
Inherent variation in the variable
Imperfect measurement equipment/ technique
The same variables arising from the same questions may be biased in different ways
response bias = what interviewer wants
prestige bias = what appears favourable
recall bias = prospective/ retrospective
What if there is missing data in key variables?
Compare participants with complete and missing data
Create a missing category for missing measurements
Interpolate what the missing measurements might have been
